NASHVILLE, Tenn. - Vince Young tried to walk off the field, then slumped back to the ground in pain from a sprained knee.

Losing a franchise quarterback is a blow from which most NFL teams can't recover.

It's only made these Tennessee Titans better.

They are one of only three undefeated NFL teams, off to their best start ever at 4-0 in a season that could have been derailed by Young's injury and bruised ego. Coach Jeff Fisher used that as his excuse to turn the offense over to veteran Kerry Collins, filling the biggest hole this team had.

And the rest of the Titans? Call it the Pacman effect. They became experts at focusing on football and ignoring soap opera while playing with cornerback Adam Jones before his trade to Dallas in April. So having help from SWAT officers and crisis negotiators to check on the quarterback's emotional well-being is nothing.

"We've been able to keep our focus despite the distractions," Pro Bowl end Kyle Vanden Bosch said.

Their success shouldn't be that much of a surprise. This team has won seven straight regular-season games going back to the end of last season, and a victory Sunday at Baltimore (2-1) would match their longest winning streak since 2000 when they had the NFL's best record.

"We've been prepared for the unexpected," Fisher said. "I think that gives you a chance to win."

Under Fisher, the Titans' winning formula involves stingy defense, a strong run game and a good kicker. Those pieces came together last season as they went 10-6 and won the AFC's last wild-card berth.

But needing to fix an offense intercepted 17 times and ranked 27th in passing, Fisher fired Norm Chow and brought back Mike Heimerdinger. The Titans also drafted running back Chris Johnson, and his 4.24-second speed in the 40-yard dash provides a breakaway threat this team has never had.

Despite lots of salary cap space, the Titans didn't waste money in free agency. They signed Jake Scott away from AFC South rival Indianapolis to replace retired right guard Benji Olson and took a chance on defensive end Jevon Kearse.

Most of their money was spent quietly on leading receiver Justin Gage and ensuring key pieces drafted over the past three years will stick around with extensions for left tackle Michael Roos, right tackle David Stewart and cornerback Cortland Finnegan — Jones' replacement and now the NFL's interception leader.

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But the key to how far this team might be able to go is the quarterback, and Young looked lost even before hometown fans started booing him in the opener. The Titans had talked all offseason of how hard Young worked to improve his footwork and his ability to read defenses and find the open receiver.

Then came the full meltdown as Young refused to go back into the opener after his second interception. He went back out and hurt his knee. But he skipped an MRI exam the next day even after Fisher went to his home to talk to his quarterback.

That was all the opening Fisher needed.